Topic: Twin Mustang.

Hi all,
       I cant pretend that the Idea is mine as there are a few currently either underway or being planned, but today has seen the start of the Twin mustang for me. Most of the centre section is done except for the top sheeting until I can decide on how I'm going to install the radio ie two receivers and extensions to the ailerons or one running 4 'Y' leads from the centre section outwards.

The more I look the better twin receivers sound but I'm not sure if this will present problems or not, any thoughts on the subject will be greatfully received.

Mine will be a cartoon scale-ish sort of made up of two ready to cover mustangs (Both 32 powered of course), With a 14 inch centre section which is built up using 3mm light-ply ribs, spruce spars, light-ply full length webbing and fully sheeted.

The horizontal stabilizer after much thought will be a lamination of 3/16, 32nd ply and 3/16 shaped to an aerofoil  section and having an HS82mg let into the stab flat. This is then covered with a blister.
I could find no other way of doing this without all sorts of 'orrible push rods waving around in the breeze.

Anyway that's the story so far I'll keep you posted as it progresses. Now then who fancies doing a twin Spitty or Me109 just for kicks? you never know we might even get a racing class for twins.

How about doing a triple???

I'll look forward to seeing it fly when do you hope to start?

2 recievers will be no bother,   just keep the ariels apart,   this will also give you the chance to cross connect,  run one with left aileron, right elavator, and and vice versa,   give you a fighting chance of one goes down

2 x 32's!!!  wow! can i have a go

a twin 109 is of course, scale...

Pictures please Daren.
Dizz

Yep should be ballistic. but I think I'll glass the wing just in case. Course you can Dave, If it lives long enough!!! However the you bend it you mend it rule applies as I'm not sure how many ARTC's are left .
I thought it might look good in the Budweiser scheme or as they were used as nightfighters in black maybe the repsol honda.

Or maybe half honda half Suzuki Rizla so it can race itself?  

Pictures please Daren.
Dizz

There's only the centre section so far dizz but as things progress I'll take some photos.

I have one of these

http://www.stevewebb.co.uk/index.php?pid=A069&area=Aircraft

Flys supurb when both motors are running and the sound of a twin flat out on a fast low pass is excellent.

Its problems are its weight which make it a major handful on one engine, it just wants to flick and spin. When I flew it recently one engine cut after take off and before I got it down the other one started to overheat and loose power so she ended up not making it back to the strip and finding a bush to land in. Minimal damage but I haven't got round to fixing her yet.

It also has a centre flap which was very useful for landing so I can suggest adding one.

 

Looks great. right size for the os32sx as well. I'll have to give the flap a miss tho as the center section will be full of cables.

Well, I've just installed the servo leads and made a well for them to sit in before joining the wing to the centre section. next job is to fit a block each side of this to take the wing bolts.

The twin Mustang doesnt have the flared leading edge that the normal one does so a little butchery of the fuz is necessary to move the wing bolt plate rearwards. This may mean installing the tank first. Hmmm...

The pics below show the installation of the servo lead to the wing. The plug is fixed to the side of the well so that I can plug it straight in and get access as necessary.

I have not got quite as far as Daren and i am still in two minds as to wether i should use two 25s or 32s. I would like to use 32s ideally but i am concerned about too much weight up front. I do not want to add any dead weight to the tail so i am going to what i can do with regards to radio placement. I have tested the twin reciver layout at great length and have come across no problems at all. Mine is going to be a Twin Voodoo, as i have always loved that colour scheme. I am using ARTCs for the project, the full size was stretched from the standard mustang but i am unable to do this with ARTCs. The nose profile is also different due to Allison engines and i will be copying this. . . . i am not going to mad as a Twin Voodoo is not scale anyway! but this model is going to provide the data for a scale job at a later date which is being worked on quietly in the background.

considering where a battery normally sits in a ARTF i don't see why two 32's would make any difference, theres still two tails out the back.

and as you have it but the front of the wing, theres the rear end to use, rudder and elevator servos out there too maybe if required.

I really dont think that there will be much if any difference in weight at the front as Cactus says all dimension are very similar. Also I think the servo at the rear will take care of any slight diferences. and there is acres of room to fit the flight pack further back. As standard mine sits right behind the tank.

Well it appears that one of the ATS 6oz tanks will fit straight in so no problems. The blocks for the bolts are in and the centre section skinned.
I used slightly thicker obechi for the spars which has meant slimming down of the wing joiner on one side to fit snugly.
The whole assembly went together quite well so far which is a result.

The xt task is to infill the servo well halves that are pre cut into the roots of the wing and then to square up both fuselages ready for the air scoops which house the mounting dowels.

In the pics below you can get some idea of the size increase to expect, Suprisingly large!!!.

More to do later, I'm off flying now.  :cig

That looks great.  Should go like stink on two 32s

Does anybody know what the difference in performance is/ how it's worked out between say a 64 sized engine (Iknow they dont exist) and two32's. I realized that the efficiency of two is far better but by how much? Is there a way of working it out and if so how?

Surely two engines are less efficient not more.  For starters you've got two lots of noise which is lost energy.  Two lots of prop inefficiencies instead of one.  Also the single larger engine would be able to spin a larger prop which would be more efficient anyway.

Sadly not so sir, Performance is significantly better with two engines. However maybe 'efficient' is a poor choice of words to describe what I mean. Power per cubic inch may be better.

shouldn't that mean a mossi can out pace a Spit, and the lanc blow both away? given they all had the same engine....

Where's PDR when you need him 

That argument cant work. They're all different aircraft built for different purposes and all possibly differently propped/geared etc. Although the mossie was no slouch.

The discussion is more about would the Spit be better with two engines the same or one bloody great engine taking into account the extra surface area of moving parts at larger sizes and for example at twice the stroke length of the pistons each revolution of the crank would take x amount longer and all that old guff.

I'm reliably informed that two are better than one big one (ask any bored housewife).

You need to think Lancaster with eight engines ::cc

yes, but your adding engines, not whole airframes. although you have in effect dropped about 3/4 of a wing....

exactly so les weight and drag= the available power has more effect.
a 60 engine turns the say 12 or 13x7 prop at 11-12000 Rpm. I'm using two 32 sized engines to turn two 9x6's at 16000 rpm each that's 2x thrust for lotts less drag and a little less weight per pound of thrust. I'm no mathematition but that has to work better.

you'll just have to race a standard one...

It's not for racing just for fun and slots.

Look what I found:

Testing Times

By February 1941, the first official test flight took place over Boscombe Down. The sceptics attended, but even they were impressed when the plane reached a top speed of 392mph, as even the newest Spitfire could only manage 374mph. The Mosquito became the fastest plane that Bomber Command had and remained so until 1951. The demonstrations even impressed the American contingent present, but when General Henry Arnold took the idea back to the US and proposed it to a group of their aircraft manufacturers, the opposition was unanimous:

The mosquito did cream the spitfire by 18 mph.

Origional report is here:

http://www.bbc.co.uk/dna/h2g2/A10533025

Look what I found:

Testing Times

By February 1941, the first official test flight took place over Boscombe Down. The sceptics attended, but even they were impressed when the plane reached a top speed of 392mph, as even the newest Spitfire could only manage 374mph. The Mosquito became the fastest plane that Bomber Command had and remained so until 1951. The demonstrations even impressed the American contingent present, but when General Henry Arnold took the idea back to the US and proposed it to a group of their aircraft manufacturers, the opposition was unanimous:

The mosquito did cream the spitfire by 18 mph.

Origional report is here:

http://www.bbc.co.uk/dna/h2g2/A10533025

I'm no expert but didn't the mossies run 2 Merlin's to the spits 1.

You are talking about 2 engines the equivalent size of one larger one. I don't think this can be more efficient.

Anyway as far as props go one large blade is more efficient than 2 smaller blades.

My only experiance that relates to this debate is my Extra Slim Twin. It has 2 x 38's and prophangs with absolute ease. The weight of the model is more than I would expect a decent single 60 size engine to prophang or give any where near the same performance.

 

exactly so les weight and drag= the available power has more effect.
a 60 engine turns the say 12 or 13x7 prop at 11-12000 Rpm. I'm using two 32 sized engines to turn two 9x6's at 16000 rpm each that's 2x thrust for lotts less drag and a little less weight per pound of thrust. I'm no mathematition but that has to work better.

The center 30& of the blades basically do nothing however I'll ignor this at the moment for simplicity.  If you increase the pitch of the prop by a factor of one you get that factor of one increase in thrust.  Increase the diameter by a factor of one and you get a thrust increase to a factor of 4 due to pie x r squared.  Therefore two 9 x 6's would give: -


   Air volume moved = (Pie x (4.5 x 4.5)) x 6
                           = 63.6 x 6
                           = 381 cubic inches

With one 18 x 6 you get: -

   Air volume moved = (Pie x (9 x 9)) x 6
                           = 81 x 6
                           = 486 cubic inches

A larger volume of air moved (assuming the same rpm) = more thrust

However I suppose this doesn't mean more speed as the speed is related to the pitch of the blade.  The larger single engine "should" be able to turn a higher pitch prop.

At the same rpm the 9 x 9 would have a much higher tip speed, can't be bothered to remember how to calculate it as I would probably fail 

I fear its alot more complicated and needs a PDR explination.

At the same rpm the 9 x 9 would have a much higher tip speed, can't be bothered to remember how to calculate it as I would probably fail 

I fear its alot more complicated and needs a PDR explination.

Think you mean a 9 x 6 and no it wouldn't have a higher tip speed at the same RPM.

Speed = Distance / Time

Tip distance covered by the 9 x 6 is Pie x D
                           = Pie x 9
                           = 28.27 inches

You can ignor the time factor as you are stating they have the same revs per minute

Tip distance covered by the 18 x 6
                            = Pie x 18
                            = 56.55 inches

The tips of the larger prop cover twice the distance of the prop half its size.  Therefore they are going at twice the RPM

The tips of the larger prop cover twice the distance of the prop half its size.  Therefore they are going at twice the RPM

Lol, that exactly what I ment but when I first read it I thought you were comparing a 4.5" prop to a 9" but as this was the radius and not diameter 

I have hopefully inlisted the help of and expert on this one. More later.

We seem to be getting away from the point a bit.  In response to gir8's comment the Mossie scenario was answering Cactus's earlier post and not particularly relevant to this.

It's not so much the efficiency of props etc. that I mean. What I'm saying is that a twin would go much better than with a single engine of twice the capacity or why would they bother making twins in the first place.

I do not mean that the props would be more efficent or use less fuel. I'm talking about the results over all. Although I'm pretty sure that two 32's would move more air at 16,000 rpm the one 60 turning a 13x6 at 11-12,000 rpm

Here is a quote from the said expert who for now wishes to remain annonymous. That said heis an engine man of some note.

"I'll have a look but basically two engines of commensurate size are infinitely more efficient than one of twice the size (all down to prop area etc) so a twin will 'go like f*ck' (technically)!"
 
cheers.

Can you guess who it is?

OK so why are all the winners at Reno single engined planes and not twins like the tigercat and p-38?

The only real way to figure this one out is to power yours with the 32's and a single engined one with the equivalent 60. And have a Reno type race.

I would be pretty confident the 60 powered version would be faster but the twin may have better vertical depending on weight and drag.

From looking at fullsize planes they go for more engines to lift more weight not to go faster.

Hmmm.. and this is only a guess mind, but the single engined ones are in one class of racing and the twins either dont race or are in a class of their own.

Ok your on!! if someone builds a twin mustang with a 60-70 2c on board from the ATS ARTC funfighters range and a 14" centre section and is only driving the one prop with no gearbox, I'll organize the race on a proper RENO 300 pylon course with independant marshalls and time keepers and we'll see which one wins.

And to be double fair two independant pylon pilots of eqal ability.

as for the full size plane I kind of agree with you, but why not just fit an engine of twice or four times the size (I suspect it might break the airframe in some way.
In fact the only one I can think of is the Antonov AN-2 which I heard has problems getting a permit to fly in some countries. (I cant confirm this and dont know why?)

Hmmm.. and this is only a guess mind, but the single engined ones are in one class of racing and the twins either dont race or are in a class of their own.

as for the full size plane I kind of agree with you, but why not just fit an engine of twice or four times the size (I suspect it might break the airframe in some way.
In fact the only one I can think of is the Antonov AN-2 which I heard has problems getting a permit to fly in some countries. (I cant confirm this and dont know why?)

I believe the twins run alongside the singles not sure if there are any still flying now though.

The AN-2 is that great big ugly biplane is it not?

Now although I don't have one I have a thing for biplanes but that one is just plain butt ugly. :laugh:

I think the main reason for multiple engines is the size of prop needed on one massive single engine.

And multiple engines give you a Little bit of redundancy should one fail.

I'm off to find the link to the vid on youtube of the tigercat racing a mustang I think it was which has nothing to do with this thread really it's just an amazing vid.

http://www.youtube.com/watch?v=m1kkilBoA3I

Have a look at that and make sure the volume is right up.

The sound will make hair stand on end that you didn't even know you had and if it doesn't I hope you have made a will out because you are dead already.